Crystal Field Interaction Research Articles

Comparative VUV Synchrotron Excitation Study of YAG: Eu and YAG: Cr Ceramics

Using synchrotron radiation, a comparative VUV excitation study of YAG ceramics doped with Eu3+ and Cr3+ ions under VUV excitation (10.5–3.7 eV) at 9 K was conducted in this work. Both ceramics exhibit distinct excitation peaks in the VUV region, indicating high-energy transitions related to the internal electronic levels of the dopants and interband transitions within the YAG matrix. For YAG:Eu, the main excitation peaks at 6–7 eV correspond to transitions within the 4f-shell of Eu3+ and Eu3+-O2− charge transfer states, showing weak dependence on the crystal field and high energy conversion efficiency. In contrast, YAG:Cr shows broad excitation bands due to transitions between levels influenced by strong crystal field interactions, resulting in lower luminescence efficiency. The study highlights the importance of crystal structure and dopant interactions in determining the spectral characteristics of YAG-based ceramics, offering potential for their application in advanced optoelectronic devices.

Growth of Ba2CoWO6 single crystals and their magnetic, thermodynamic and electronic properties

This study explores the bulk crystal growth, structural characterization, and physical property measurements of the cubic double perovskite Ba2CoWO6(BCWO). In BCWO, Co2+ions form a face-centred cubic lattice with non-distorted cobalt octahedra. The compound exhibits long-range antiferromagnetic order belowTN= 14 K. Magnetization data indicated a slight anisotropy along with a spin-flop transition at 10 kOe, a saturation field of 310 kOe and an ordered moment of 2.17µB atT= 1.6 K. Heat capacity measurements indicate an effectivej= 1/2 ground state configuration, resulting from the combined effects of the crystal electric field and spin-orbit interaction. Surface photovoltage analysis reveals two optical gaps in the UV-Visible region, suggesting potential applications in photocatalysis and photovoltaics. The magnetic and optical properties highlight the significant role of orbital contributions within BCWO, indicating various other potential applications.

Spin-1 Antiferromagnetic Heisenberg Model Including Dzyaloshinskii-Moriya Interaction

The spin-1 antiferromagnetic Heisenberg model was investigated by the introduction of spin operators on a square lattice in terms of a mean-field approximation (MFA). The bilinear exchange interaction parameters Jx and Jz, the crystal field interactions Dx and Dz, and the external magnetic field components Hx and Hz along the x- and z-axes were all incorporated in the model Hamiltonian. The effects of the Dzyaloshinskii-Moriya interaction (DMI), ∆m, were also included along the y-axis, i.e. containing the spin components only along the x- and z-axis. Various phases of the model, including ferromagnetic (FM), antiferromagnetic (AFM), and random (R) were identified by studying the thermal variations of the order-parameters, susceptibilities, specific heats, and free energy of the sublattices. The second-order phase transition temperatures between these phases were identified, in addition to the existence of first-order phase transitions. Numerous critical points, including the three-phase coexistence, were observed on the phase diagrams. The reentrant behavior was also seen for appropriate values of the system parameters.

Engineering Clock Transitions in Molecular Lanthanide Complexes.

Molecular lanthanide (Ln) complexes are promising candidates for the development of next-generation quantum technologies. High-symmetry structures incorporating integer spin Ln ions can give rise to well-isolated crystal field quasi-doublet ground states, i.e., quantum two-level systems that may serve as the basis for magnetic qubits. Recent work has shown that symmetry lowering of the coordination environment around the Ln ion can produce an avoided crossing or clock transition within the ground doublet, leading to significantly enhanced coherence. Here, we employ single-crystal high-frequency electron paramagnetic resonance spectroscopy and high-level ab initio calculations to carry out a detailed investigation of the nine-coordinate complexes, [HoIIIL1L2], where L1 = 1,4,7,10-tetrakis(2-pyridylmethyl)-1,4,7,10-tetraaza-cyclododecane and L2 = F- (1) or [MeCN]0 (2). The pseudo-4-fold symmetry imposed by the neutral organic ligand scaffold (L1) and the apical anionic fluoride ion generates a strong axial anisotropy with an mJ = ±8 ground-state quasi-doublet in 1, where mJ denotes the projection of the J = 8 spin-orbital moment onto the ∼C4 axis. Meanwhile, off-diagonal crystal field interactions give rise to a giant 116.4 ± 1.0 GHz clock transition within this doublet. We then demonstrate targeted crystal field engineering of the clock transition by replacing F- with neutral MeCN (2), resulting in an increase in the clock transition frequency by a factor of 2.2. The experimental results are in broad agreement with quantum chemical calculations. This tunability is highly desirable because decoherence caused by second-order sensitivity to magnetic noise scales inversely with the clock transition frequency.

Compensation behavior for a mixed spin-3 and spin-7/2 Blume–Capel system with crystal field interaction

In this article, we studied compensation points in a spins system represented by the Hamiltonian of Blume–Capel of spin-3 and spin-7/2 in a square lattice. Free energy and equations of state were obtained using mean field theory via Bogoliubov inequality. The second-order phase transition was studied in a narrow range of temperature values and single ion anisotropies, in addition to the existence of compensation points within this range. We used the mean-field theory approximation to study compensation points through total magnetization and performed a Monte Carlo Simulation (MCS). In this way, we show the existence of compensation points via mean field and MCS.

Magnitouprugost' yan-tellerovskoy podsistemy v kristallakh tipa AIIBVI, dopirovannykh khromom

The influence of an external magnetic field on the complex elastic moduli of crystals with a sphalerite or zinc blende (ZnSe) and wurtzite (CdSe) structure lightly doped by Cr2+ ions has been investigated. Measurements have been performed in the frequency interval 26–32 MHz at 1.4 K. In II–VI crystals, bivalent chromium cations are triply orbital-degenerate in the ground state and, being in a tetrahedral environment, produce Jahn–Teller complexes. These complexes are described in terms of the T ⊗ (e + t2)-problem and exhibit the adiabatic potential energy surface with the global minima of tetragonal symmetry. It has been found that in ZnSe:Cr2+ crystals, a magnetic field directed along the [001] and [110] axes influences modulus (c11 – c12)/2 and does not influence modulus c44. In CdSe:Cr2+ crystals, however, moduli c55 and c66, which are the analogs of (c11 – c12)/2 and c44, depend on the magnetic field directed along the [101¯0101¯0] and [21¯1¯021¯1¯0] axes, respectively. The discovered anomalous behavior of the elastic moduli with magnetic field has been treated in terms of a model that takes into account the crystal field, vibronic and spin-orbital interactions, and the contribution of the Jahn–Teller subsystem to isothermal moduli determined at a constant magnetic induction. Good agreement with experimental dependences of the elastic moduli in strong magnetic fields has been obtained, and it has been shown that the nonmonotonic variation in weak magnetic fields (below 2 T) should be associated with a magnetic field dependence of the relaxation time.

Dynamic study of a ternary trilayer Ising system with crystal field interaction

Dynamic study of a ternary trilayer Ising system with crystal field interaction

Magnetic circular dichroism in the dd excitation in the van der Waals magnet CrI3 probed by resonant inelastic x-ray scattering

We report on a combined experimental and theoretical study on ${\mathrm{CrI}}_{3}$ single crystals by employing the polarization dependence of resonant inelastic x-ray scattering (RIXS). Our investigations reveal multiple Cr $3d$ orbital splitting ($dd$ excitations) as well as magnetic dichroism (MD) in the RIXS spectra. The $dd$ excitation energies are similar on the two sides of the ferromagnetic transition temperature, ${T}_{C}\ensuremath{\sim}61$ K, although MD in RIXS is predominant at 0.4 T magnetic field below ${T}_{C}$. This demonstrates that the ferromagnetic superexchange interaction that is responsible for the interatomic exchange field is vanishingly small compared with the local exchange field that comes from exchange and correlation interaction among the interacting Cr $3d$ orbitals. The recorded RIXS spectra reported here reveal clearly resolved Cr $3d$ intraorbital $dd$ excitations that represent transitions between electronic levels that are heavily influenced by dynamic correlations and multiconfiguration effects. Our calculations taking into account the Cr $3d$ hybridization with the ligand valence states and the full multiplet structure due to intra-atomic and crystal field interactions in ${\mathrm{O}}_{h}$ and ${\mathrm{D}}_{3d}$ symmetry clearly reproduced the dichroic trend in experimental RIXS spectra.

Triggering single-molecule qubit spin dynamics via non-Abelian geometric phase effects.

We illustrate how macroscopic rotations can be utilised to trigger and control a spin dynamics within the ground doublet of both Kramers and non-Kramers-type molecular nanomagnets via the non-Abelian character of the time-evolution operator. For Kramers magnets, we show how this effect can be harnessed to realise single-qubit quantum gates and give the explicit example of a recently reported CoCl2(tu)4 single-molecule magnet (SMM). We demonstrate that gating operations could be performed on this magnet in as fast as 10 ps before the breakdown of adiabaticity, much faster than typical spin-lattice relaxation times. Based on this effect, we also suggest CoCl2(tu)4 as a quantum gyroscope for sensing yaw-axis rotations. For integer spin nanomagnets where non-axial crystal field interactions often lift ground state degeneracy, we show how spin dynamics from the non-Abelian geometric propagator can be recovered using non-adiabatic macroscopic rotations not-necessarily resonant with the tunnel splitting gap. Using the well-known TbPc2 single-ion magnet as a further example, we identify an experimentally plausible non-adiabatic rotation that induces a coherent superposition of tunnelling ground states, tantamount to preparing each member of a TbPc2 ensemble in the maximal angular momentum state |mJ = 6〉. The detection of an ensuing coherent oscillation of the macroscopic magnetisation polarised along the TbPc2 principal magnetic axis after the completed rotation could then proceed via time-resolved magnetisation measurements.

Kondo quasiparticle dynamics observed by resonant inelastic x-ray scattering

Effective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd3 to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature—the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.

Time oscillating magnetic field effect on critical behavior and dynamic phase transition of monolayer nanographene structure

ABSTRACT Dynamic magnetic properties of a ferrimagnetic mixed (1/2,1) Ising spin monolayer nanographene structure with a crystal-field interaction in a time oscillating magnetic field are studied by the use of the kinetic Monte Carlo simulation based on the Metropolis algorithm. Dynamic phase transitions are obtained, the effect of the next-nearest neighbor interactions, the crystal field, the amplitude, and the period of the external dynamic magnetic field on the critical and compensation behaviors and on the thermal variations of the dynamic order parameters are investigated. We have found that in the presence of the time oscillating field, the system may exhibit a dynamic phase transition from the ferrimagnetic to the paramagnetic phase at a critical point. The system may even present two dynamic compensation temperatures for appropriate values of the hamiltonian parameters. This behavior of dynamic compensation temperature has not been observed previously in published papers with kinetic Monte Carlo simulation.

Compensation and Critical Behavior of Mixed Spin Ising Model with Four-Spin Interactions in a Crystal Field

We study the thermodynamical properties of two-dimensional mixed spin Ising system consisting of spin-[Formula: see text] and spin-1 with four-spin interactions in crystal field interactions on a square lattice within the framework of the finite cluster approximation based on single-site cluster theory. In this paper, the phase diagrams show qualitatively and quantitatively interesting features. In fact, the system exhibits a variety of interesting features resulting from the introduction of the four-spin interactions and the crystal field interactions. Finally, using the same method, we study the behavior of the total magnetization of the Ising model with four-spin interactions in the crystal field to show the existence of compensation points and point intervals for certain values of [Formula: see text].

Nonequlibrium magnetic features in a mixed spin (2, 5/2) Ising system driven by the external oscillating magnetic field by path probability method

Utilizing the path probability method, we investigated nonequilibrium magnetic features in a mixed spin (2, 5/2) Ising model Hamiltonian composed of bilinear and crystal-field interactions in the presence of an external oscillating magnetic field. We numerically solved the time dependence of average magnetizations to find the phases in the system. We examined the dynamic magnetizations to obtain dynamic phase transition (DPT) temperatures, the nature of the DPTs, and phases in the system. The dynamic phase diagrams (DPDs) were constructed in reduced temperature and the amplitude of oscillating magnetic field plane for various interaction parameters. We observed that the system gives very rich and interesting topological behaviors of DPDs, such as up to two dynamic tricritical points, six critical end points, a double critical end points, a zero-temperature critical point, one inverse critical end point and a quadruple point depending on interaction parameters. The system also exhibits paramagnetic, six distinct ferrimagnetic and three different nonmagnetic phases as well as up to eleven different mixed or hybrid phases. In addition, the system exhibits the reentrant behavior.

Anisotropy of the Magnetic Properties of Er³⁺ Ion in Erbium Iron Garnet Crystal at Low Temperature

With the consideration of crystal field (CF) and exchange interaction between the magnetic ions, we conduct a theoretical analysis to the anisotropy of the magnetization caused by Er^3+ ions in erbium iron garnet (ErIG) in the temperature range from 4.2 to 150 K. It is found that the anisotropy of the magnetization caused by Er^3+ ions originates mainly from the anisotropic Er^3+–Fe^3+ ion exchange interaction. In the course of research, a set of relatively suitable CF parameters are obtained by analyzing the influence of different CF parameters on the magnetization. The secular equation is solved by quantum theory after taking into account the coupling of the ⁴I_15/2 and ⁴I_13/2 multiplets, and the energy levels and wave functions of Er^3+ ions are further obtained. Then, the magnetization of Er^3+ ions at six inequivalent sublattices when magnetized along the [100], [110], and [111] directions are calculated, respectively. Following this, comparisons between the average value of the so-obtained six quantities and the experimental data are made in the [100], [110], and [111] magnetization directions. The calculated results coincide well with the experimental data and [100] is the easy magnetization direction.

Crystal-field effects competing with spin-orbit interactions in NaCeO2

Ce compounds feature a remarkable diversity of electronic properties, which motivated extensive investigations over the last decades. Inelastic neutron scattering represents an important tool for understanding their underlying electronic structures but in certain cases a straightforward interpretation of the measured spectra is hampered by the presence of strong vibronic couplings. The latter may give rise to extra spectral features, which complicates the mapping of experimental data onto standard multiplet diagrams. To benchmark the performance of embedded-cluster quantum chemical computational schemes for the case of $4f$ systems, we here address the Ce 4$f^1$ multiplet structure of NaCeO$_2$, an antiferromagnet with $D_{2d}$ magnetic-site symmetry for which neutron scattering measurements indicate only weak vibronic effects. Very good agreement with the experimental results is found in the computations, which validates our computational approach and confirms NaCeO$_2$ as a 4$f$ magnet in the intermediate coupling regime with equally strong 4$f$-shell spin-orbit and crystal-field interactions.

Random Crystal Field Effect on the Critical Properties of the Mixed Spin-(52,12) Anisotropic Heisenberg Model in the Oguchi Approximation

We have employed the Oguchi approximation (OA) to investigate the effects of a random crystal field which is active (inactive) with probability [Formula: see text] [Formula: see text] for given lattice sites on the thermodynamic properties of the mixed spin-[Formula: see text] anisotropic Heisenberg model in the presence of an external magnetic field. By exploiting the thermal variations of the order parameters, interesting phase diagrams are produced on various planes. The phase diagrams show first- and second-order transition lines and also tricritical points. In addition to the reentrant behavior which is localized in a certain range of [Formula: see text] at very low temperature, the magnetic exponent [Formula: see text] calculated near the critical point exhibits interesting behaviors depending on the crystal field interaction. The hysteresis behavior of the model is also investigated and it reveals that the width of hysteresis loop decreases or increases, respectively, for negative or positive crystal field region as the probability [Formula: see text] increases.

Dynamic multicritical phase diagrams of the mixed spin (2, 5/2) Blume-Emery-Griffiths model with repulsive biquadratic coupling

We investigated the dynamic phase transitions (DPTs) in the mixed spin (2, 5/2) Blume-Emery Griffiths model with repulsive biquadratic interaction in the presence of a time-varying magnetic field. We used the path probability method to obtain the set of the dynamic equations. We numerically solved these dynamic equations to characterize the nature of first- and second-order phase transitions and to find the DPT temperatures as well as obtain the phases in the system. We constructed the dynamic phase diagrams (DPDs) in reduced temperature and amplitude of oscillating magnetic field plane. We observed that the DPDs display richer, complex and more topological various type of phase diagrams. In particular, DPDs exhibit the disordered phase, antiquadrupolar or staggered phase, six different ferrimagnetic phases, three different nonmagnetic phases, and numerous mixed phases. DPDs also display two dynamic tricritical points for only smaller values of crystal-field interactions, multiple critical end and double critical end points, one zero-temperature critical point, one inverse critical end point, and a quadruple point depending on interaction parameters. The system always shows the reentrant behaviors for the higher values of magnetic field amplitude, but it does not exhibit the dynamic tricritical behavior for higher values of crystal-field parameter.

Solid solution Na(Gd/La)(MoO4)2:Yb3+/Er3+ upconversion nanocrystals with simultaneously enhanced photothermal conversion efficiency and luminescence intensity

Lanthanide doped upconversion nanocrystals with remarkable optical properties have been utilized for many emerging applications. Here, solid solution Na(GdxLa1-x)(MoO4)2 nanocrystals are synthesized hydrothermally, and their upconversion photoluminescent and photothermal properties as luminescent host matrix for Yb3+/Er3+ activators are systematically studied. The effect of La3+ doping content on the phase, crystal structure, upconversion luminescence and photothermal conversion are investigated. Rietveld refinements based on XRD data indicate that La3+ occupy Gd3+ sites substitutionally, and pure phase solid solution Na(GdxLa1-x)(MoO4)2 is formed. Due to lattice distortion, lower lanthanide site symmetry and augmented odd-parity crystal field interactions after La3+ doping, the 4f-4f transition probabilities of the lanthanide ions are effectively increased. Na(Gd/La)(MoO4)2 solid solution hosts exhibit enhanced upconversion luminescence from Er3+/Yb3+, compared with single-component NaGd(MoO4)2 counterparts. What's more, based on the calculated temperatures of the samples derived from the luminescence intensity ratio of states 2H11/2 and 4S3/2 for Er3+, enhanced photothermal conversion efficiency is speculated in solid solution Na(GdxLa1-x)(MoO4)2:Yb3+/Er3+ nanocrystals, which is further confirmed by infrared thermographic images. The underling mechanisms of simultaneously enhanced photothermal effects and luminescence intensity in Na(GdxLa1-x)(MoO4)2 solid solution nanocrystals are elucidated. Modulation of composition in solid solution hosts may be an effective method for combating luminescent thermal quenching and/or regulating photothermal conversion and photoluminescence properties simultaneously. Multifunctional solid solution upconversion nanocrystals could be potential for photoluminescent and photothermal applications.

Anomalous magnetism of uranium(IV)-oxo and -imido complexes reveals unusual doubly degenerate electronic ground states

Anomalous magnetism of uranium(IV)-oxo and -imido complexes reveals unusual doubly degenerate electronic ground states

Magnetic properties and magnetic phase transition in square-octagon lattice: Monte Carlo study

ABSTRACT The magnetic properties and magnetic phase transition in square-octagon lattice with mixed spins 3/2 and 5/2 were investigated by Monte Carlo simulations. The ground state phase diagrams of square-octagon structure were obtained under the effect of crystal field and exchange interactions. The thermal partial, total magnetizations and magnetic susceptibilities of square-octagon lattice are obtained for a fixed magnetic parameter. The reduced Néel temperature is noticed. The variation of total magnetizations with the crystal field of square-octagon structure is shown. The magnetic hysteresis cycle of square-octagon structure, with mixed spins S = 3/2 and σ = 5/2 for several exchange interactions, temperatures and crystal fields, is found.